System for growing concentrated populations of oysters and related shellfish

ABSTRACT

Systems are described for the forced feeding of mollusks such as free oyster and clam seed employing rafts or a flume, having means holding the free oyster or clam seed. Water containing nutrients is forced upwardly through the free oyster or clam seed to feed a dense population thereof by tide flow in a system operating below water level. The rafts are anchored to take advantage of the tide flow. Baffles graduated in length from the forward end to the rear are provided at spaced intervals, transverse to the direction of the incoming tide flow. These baffles extend downwardly at a forward inclined angle. The system includes trays having foraminous bottom walls in which the free oyster or clam seed rests. The upward flow of water through the oyster and/or clam population also continuously removes detritus generated.

United States Patent [1 1 Wiegardt, Jr,

[ SYSTEM FOR GROWING CONCENTRATED POPULATIONS OF OYSTERS AND RELATEDSHELLFISH [76] Inventor: John L. Wiegardt, Jr., Box 16,

Nahcotta, Wash.

[22] Filed: Nov. 8, 1971 [21] Appl. No.: 196,684

[52] US. Cl. 119/4 [45] Oct. 23, 1973 Primary Examiner-Russell R. KinseyAssistant Examiner-James H. Czerwonky Att0rney-Richard W. Seed et al.

[57] ABSTRACT Systems are described for the forced feeding of molluskssuch as free oyster and clam seed employing rafts or a flume, havingmeans holding the free oyster or clam seed. Water containing nutrientsis forced upwardly through the free oyster or clam seed to feed a densepopulation thereof bytide flow in a system operating below water level.The rafts are anchored to take advantage of the tide flow. Bafflesgraduated in length from the forward end to the rear are provided atspaced intervals, transverse-to the direction of the incoming tide flow.These baffles extend downwardly at a forward inclined angle. The systemincludes trays having foraminous bottom walls in which the free oysteror clam seed rests. The upward flow of water through the oyster and/orclam population also continuously removes detritus generated.

5 Claims, 9 Drawing Figures Pmmnnbm 23 1975 SHEET 0F 5 FIGJS FIG 7PATENIED I6! 23 I975 1 SYSTEM FOR GROWING CONCENTRATED POPULATIONS OFOYSTERS AND RELATED SHELLFISH BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates to a system for the artificialgrowing of mollusks such as free oyster and clam seed, either in raftsanchored in tidal flow areas or in a flume system.

2. Prior Art Relating to the Disclosure Oysters, in their natural state,reproduce by spawning free swimming larvae that diffuse into the watermedium. After a time for development, usually several weeks induration,,the larvae attach to suitable materi-- als, usuallyclean,,hard objects such as rocks and oyster shells. The natural home ofthe oyster is thus usually an oyster reef where oysters continuallyattach themselves to the shells of their predecessors, or a rocky beachor ledge. In these areas, the same currents that carry the oyster larvaecarry the plankton to the attached oyster from which he derives hisfood.

The reproductive cycle of the oyster has been used to advantage by manby placing cultch" materials shells, rocks, sticks, etc. on which theoyster larvae attach, and then cultivating the resulting seed. One ofthe earliest methods of this type cultivation was to plant the cultchwith seed attached on suitable bottom areas of estuaries in populationsdense enough to permit efficient care and harvesting. Using thistype ofculture seed must be both cheap and plentiful as losses in the growingpopulation are high due to the actions of predators and silting.Further, the bottom areas are not the natural home for the oyster andfeeding conditions are usually not as good as these in natural reefs androcks where tide flows and currents are swifter. In the areas whereoysters reproduce naturally, however, the success of the setting oftenresults in overcrowding in the oyster population, both in terms of spaceoccupied and in competition for available food.

SUMMARY OF THE INVENTION This inventionprovides means of growing freeoyster and clam seed in a system which provides, through the medium ofan induced, upwelling flow of water, a sup ply of nutrients adequate tosustain maximum rates of growth and condition throughout a concentrated,dense population. In this system, smaller oysters and clams tend to siftto the lower areas of the population; however, since they have firstaccess to the upwelling nutrient-laden flow of water, they obtainadequate supplies of food, thus assuring uniform rates of growththroughout the population. Since the upwelling flow of water partiallysupports the oyster, the oyster can grow and expand in relation toothers held in similar suspension with no distortion of shape as resultsin a crowded natural" or conventional tray system. Thus, populationdensities are feasible which have never before been possible using otherculture systems and the natural tendency ofoysters and clams: to growand produce edible meats can be better controlled and utilized.

Oysters and clams can be grown to any size with the system of thisinvention, with optimum sizes dependent upon balancing of the costs ofconstructing and operating the system against the costs of implantingthe oysters in natural estuarial areas or other culture systems.

The upwelling current of water through the oyster or clam seed can bedeveloped by a number of means, including gravity pumping or tidal flow,or using, if desired, by-product water of other systems such as coolingwater from thermal or nuclear power plants. Oysters and clams can beused as filtering agents with the system of this invention to clean upalgae and plankton populations in water passing through the system.

The objects of this invention include (1) providing a flume holding aseries of trays having foraminous bottom walls on which the free oysteror clam seed rests, water being forced upwardly through the populationin the trays; (2) providing a raft holding the free seed, the raftdesigned to be anchored in an area of tide flow wherein water containingnutrients is forced upwardly To overcome the problems generated by both.natural and bottom culture and to ensure better seed survival andoyster growth, more advanced types of cultures, utilizing various meansto suspend the oyster off the bottom have been developed. These includeproviding trays, sticks or shells with seed attached. When shells areused they are generally spaced out on wires or ropes. I

Recent developments in hatchery techniques have made possible theproduction of adequate supplies of oyster and clam seed for commercialoperation regardless of natural sets. One of the results of hatcherytechnology has been the development of cultchless or free oyster seedwhere oyster seed is produced that is not attached to cultch. A methodand apparatus for growing free oyster seed is describedin U. S. Pat. No.3,517,648, wherein water containing nutrients is pumped continuouslythrough the seed population I carrying food to and detritus from theseed.

The major problem with the use of free seed has been to take it throughfrom the tiny hatchery-produced stage to a size and condition where ithas commercial value. Present hatchery technology limits the size towhich the seed can be grown feasibly because of the costs involved inthe production of food for the seed.

through the population contained in the trays to feed them and to carryaway the detritus generated; (3) providing a raft for artificallygrowing oysters and clams,

, the raft including a series of graduated baffles extending downwardlyfrom the bottom of the raft, the baffles directing the incoming tideflow upwardly through free seed contained in a series of abutting andstacked trays having foraminous bottom walls, each'tray holding a densefree seed population; (4) providing a raft for artificially growingoysters and clams wherein water containing nutrients is drawn upwardlythrough a dense population heldwithin an elongated duct; (5) providing araft for artificially growing oysters and clams utilizing power means,such as an impeller, for drawing the nutrient-containing water throughthe population;

' and (6) providing a series of nesting trays positioned along'the axisof tidal flow with a system of baffles that directs an upward flow ofwater through a portion of the population during each phase of the tidalflow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of onemeans of artificially growing oyster and clam seed utilizing a flumehaving removable trays holding the seed, the trayspositioned in thewater flow down the flume and designed to force the water upwardlythrough the bottom of the trays through the dense oyster or clampopulation resting therein;

FIG. 2 is a partial longitudinal cross-sectional view through two of theabutting trays illustrating the water flow therethrough;

FIG. 2A is a longitudinal cross-sectional view illustrating an alternatetray design;

FIG. 3 is a perspective view of a raft anchored in a tide flow regionwith a series of trays positioned therein holding oyster or clam seed;

FIG. 4 is a longitudinal cross-sectional view of the raft of FIG. 3illustrating water flow through the raft;

FIG. 5 is a partial perspective view of a series of nested trays, eachholding a dense population of seed, the trays adapted for positioning inthe raft of FIG. 3;

FIG. 6 is a longitudinal cross-sectional view of a raft employing aninclined elongated duct within which the oyster or clam population isheld;

FIG. 7 is a perspective view of a raft system utilizing an impeller toforce nutrient-containing water through a series of trays; and

FIG. 8 is a perspective view ofa modified raft design.

DESCRIPTION OF THE PREFERRED EMBODIMENTS .Referring to FIG. 1 a flumesystem is illustrated in which mollusks, either free oyster seed or clamseed, rests in a series of trays having foraminous bottom wallspositioned in the path of water flow through the flume. The flumeincludes a bottom wall 10 sloping downwardly from the point ofintroduction of the water with upended sidewalls 11 and endwalls 12. Theflume may be divided into sections at spaced intervals along the lengththereof by separators 13. At the end of each of the sections is a drain14. Within each of the sections are positioned a series of traysadjacent one another in which the oyster or clam seed rests.

FIG. 2 shows one tray design in more detail. Each of the trays 15include vertical sidewalls 16 and a foraminous bottom wall 17. At theforward end of each of the trays are. legs 18 which space the bottomwall of the tray from the bottom wall. 10 of the flume. Near the rear ofeach tray is a baffle 19 extending the full width of the trayrPreferablythe baffleis positioned just forward of therear sidewall of the tray andhas a height less than the height of the sidewalls of the tray. Each ofthe trays may be provided with a handle 20 if desired.

An alternate tray design is illustrated by FIG. 2A. Each tray 80includes three upended sidewalls 82 connected to a foraminous bottomwall 81. The rear sidewall 85 is also foraminous. Parallel legs 83extend down the length of the sidewalls of the tray. The legs 83preferably slope downwardly beginning at the front of the tray fromabout l inch to 1 inch giving a reverse slope to the bottom wall 81,thereby allowing water to flow evenly to the oyster or clam populationresting on the upper surface of the bottom wall 81. The trays may beprovided with a handle 84 for removal and insertion of the tray in thetlurne. The lower portion 86 of the rear wall of the tray forms asupport for the tray, extends the full width of the tray and is designedto act as a waterstop" to force water upwardly through the bottom wallof the tray. Preferably the rear wall portion 86 is sloped rearwardly atan angle approximating 45 to provide smooth flow of water through thetray. Longitudinally extending supports 87 secured to the bottom wall 81and the front and rear side walls may be provided to aid in supportingthe foraminous bottom wall 81. These supports should have sloped uppersurfaces to prevent seed from resting. on them.

When the trays are positioned in the path of waterflow down the flume asillustrated in FIG. 1, water entering through conduit 21 from watersupply 22, the water supply containing nutrients for the seed, isdirected into each of the sections where it flows beneath the first ofthe trays positioned therein until baffle 19 or rear wall 86 isencountered. Referring to FIG. 2 the baffle forces the water upwardlythrough the screen bottom wall of the tray over the top of baffle 19,down through the bottom wall to the rear of the baffle and to the nextabutting tray.

Withthe tray design of FIG. 2A the trays must be spaced from each othera few inches to allow water exiting through the rear wall of one tray toturn below the next adjacent tray. Oyster or clam seed 23 resting in adense population limited only by the height of trays and flume in eachof the trays is thus provided with a continuous supply ofnutrient-containing water. The water aids in carrying away the detritusgenerated by the seed. The number of trays which can be positioned insequence in each of the sectioned areas is dependent on the populationof seed in each of the trays, the rate of flow of the water through thetrays, the size of the trays and other variables. Rather than as shown,a separate water supply can be provided to the forward end of each ofthe sectioned areas containing trays instead of channeling the waterdown a side channel 24 as illustrated in FIG. 1, the water diverted tothe forward end of each of the series of trays.

The water after passing over and through the series of trays containingthe free oyster seed drains through opening 14 in the bottom wall of theflume. The water supply may be taken from any appropriate sourcecontaining proper nutrients for the oyster seed.

Oyster seed grown in the trays as described grow uniformly throughoutthe length and height of each tray. The upward flow of water containingnutrients through the dense population of oyster seed supplies nutrientsto all the oysters in the trays uniformly and permits optimum growth ofthe population.

The flurne system illustrated in FIG. 1 may be stacked one above theother in a relatively small area to enable artificial growing of greatnumbers of oyster or clam seed to an intermediate size. The flume systemis housed within a'suitable enclosure to prevent direct sunlight on theoyster beds.

FIG. 3' shows a raft system for artificially growing oysters or clams,the raft adapted to be anchored to a single anchor on which it can pivotin an area of relatively fast tide flow. The ebb and flow of the tide isutilized to force feed the seed contained in foraminous bottom walledtrays in the raft. The raft 30 includes a frame comprising verticalcorner supports 31 joined together by longitudinally extending upper andlower beams 32, and transverse beams 33. Cross beams 34 are utilized tostabilize the frame structure. Side slats 35 are used to preventsubstantial water flow through the side walls of the raft. Under each ofthe upper beams 32 or at other suitable locations are provided floats 36of expanded polystyrene or other suitable flotation material. At theforward end of the raft are disposed deflectors 37 extending across thewidth of the forward end. The deflectors aid in preventing water flowover the top of the trays resting in the raft. Instead the water isdirected under the raft and then upwardly through the trays. Referenceis made to FIG. 4 showing that the horizontal plane formed by the lowerbeams 32 and tray supports 38, is sloped downwardly from the forward endof the raft in order to achieve uniform water flow upwardly throughtrays positioned in the raft as will be described. I

Stacks of trays, preferably nested together as illus trated in FIG. 5,are rested on the spaced tray supports 38 as shown in FIG. 4. FIG. 5shows the trays 40 in more detail. Each of the trays has a foraminousbottom wall 41 sandwichedbetween upper and lower side walls 42 and 43.Referring to FIG. 5 the lower sidewall 43 may have a flange 44 extendingdownwardly therefrom which keys together with an upwardly extendingflange 45 of theupper sidewall 42 of the next adjacent tray, enablingthe trays to be nested together. The trays may be banded together withordinary strapping equipment to insure retention of seed. A cover (notshown) covers the top tray to prevent direct sunlight on the oystersresting on the upper surface of each of the trays.

The trays are held in the raft by any suitable means such as metalstraps extending across the top of the trays bolted to the sides of theraft frames and to spaced vertical supports 48 extending from the traysupports 38 at the intersecting corners of'each of the trays. The traysmay be provided with center supports 46 as necessary.

Referring to FIG. 4 baffles 47 graduated in length from the forwardendto the rear are provided at spaced intervals, transverse to thedirection of incoming tide flow upwardly through the seed resting in thetrays. The combination of the sloping bottom wall of the raft and thegraduated length baffles enables a maximum amount of water to bedeflected uniformly through the entire series of trays held in the raft.

At the rear of the raft deflector plates 49 may be provided, thedeflector plates extending outwardly from the sidewalls of the raft atan angle thereto. The deflector plates deflect water flow alongside theraft out wardly and thereby create a partial negative pressure at the.open rear end of the raft aiding the water flow upwardly through theoysters or clams in the trays and out the rear end of the raft. Thedeflector plates also help to position the raft directly in the tideflow. FIG. 4 shows the water flow pattern through the raft and trayspositioned therein. The raft is provided with a top cover to shield theoysters in the upper trays from direct sunlight and to prevent foulinggrowth. The upper tray at the forward end of the raft should bepositioned below the water level 39 at all times. The number of trayswhich can be stacked in each series is dependent on the amount of waterflow through the raft, the depth of the seed in each tray and otherfactors.

Utilizing the raftas described, oysters can be grown uniformlythroughout the trays at optimum rates and in greater densities thanheretofore possible. The raft is anchored transversely to the tide flowby suitable antrays is about 6 inches deep and is filled with oyster orclam seed.

FIG. a illustrates a raft design, the raft also adapted to be anchoredto a single anchor about which it can pivot in areas of tide flow. Theraft 70 comprises vertical corner supports 71 joined together by beams'72, both longitudinal and transverse. An elongated open ended duct ortube 73 is supported by the raft frame, the duct inclined upwardly fromthe front of the raft to the rear thereof (relative to the direction ofwater flow). The duct is completely enclosed. In the interior thereof isa mesh bottom wall 74 extending essentially horizontally relative to thewater line 75. The mesh 74 is designed to support an oyster or clampopulation on its upper surface. Water containing nutrients is drawnthrough the duct 73 and the population contained therein. Assuming theduct has dimension of about 2 feet in depth and 4 feet in width with awaterflow therethrough at about 1 mph, approximately 300,000 gallons ofwater will flow through the duct in about one hour. Floats (not shown)of expanded polystyrene foam or other suitable material are provided asillustrated by FIGS. 3 and 4 to support and stabilize the raft in thewater. This tray design affords several advantages over that illustratedby FIGS. 3 and 4 in that the top of the duct acts as the cover and theduct automatically loads with water as the waves become higher. Oysteror clam seed is loaded and unloaded from the raft by pumps which arecommercially available.

FIG. 7 illustrates a further alternate to the flume system of FIG. 1.This system utilizes an impeller or other suitable power means to forcenutrient-containing water through trays holding oyster orclampopulations, the trays held in a floating container 50. The container 50includes a bottom wall 51, vertical sidewalls 52, 53, a front wall 54and top wall 55. The rear wall is a mesh material which allows free flowof water therethrough.

The forward wall 54 is provided with an opening therein. Mounted on eachside of the outer side of the opening are guides 54a. A box-like hood 56is provided with a power driven impeller 57 mounted in the end wallthereof adjacent the front wall 54, the hood adapted to slide verticallyalong the rails 54a. The bottom wall of the vhood is open to receivewater. Suitable power means (not shown) are used to drive the impellerwhich draws water into the interior of the container 50. A suitablemechanical or power system 58 is utilized to raise or lower the hood andimpeller to determine the level at which water is drawn into theimpeller. Flotation means 59 such as expanded polystyrene are secured tothe side walls of the container. A series of nesting trays 63 havingforaminous bottom walls 64 and rear walls 62 are positioned in thecontainer. The lowermost wall 65 of the series of the trays is supportedfrom the bottom wall 51 of the container to allow adequate water flowupwardly through the trays. The unit as shown in FIG. 7 is about 7 feetlong, 8 feet wide and 4 feet deep. The trays, removable at the rear ofthe container, are about 3 feet wide and 4 feet in length. Nutrientcontaining water is driven through the trays holding oyster or clam seedby the impeller.

FIG. 8 illustrates another raft configuration adapted to be anchored tofore and aft anchors to position it along the axis of the tidal flow.The raft frame comprises vertical corner supports 91 joined by solidside walls 92 and 93 and upper and lower beams (not shown) joining theside walls together. A series of trays are stackedwithin the frame ofthe raft. Each tray has a foraminous bottom wall 94 joined to verticalside walls 95. A solid top 96 covers each of the trays and is inclinedupwardly from the front and rear of the tray to form a center apex 97. Amedian support 98 extends between the side walls of the tray. When thetrays are stacked in the raft frame the median support of each uppertray rests on the apex of the tray just beneath. The'corners of thetrays are supported by the corner supports 91. When positioned in anarea of tide flow, nutrient-containing water entering through openings99 between each tray is first deflected upwardly through a forwardportion of the bottom wall of the tray on which the free oysters orclams rest and then down through the oyster or clam population in therear portion of the bottom wall of each tray as illustrated by thearrows in FIG. 8. Flotation means (not shown) are secured to the frameto maintain the raft at the proper level.

Generally it has been found that oyster seed obtained directly from ahatchery operation (generally about 1/10 inch in diameter) can be grownto any size desired, with the timing of its removal from the flumesystem depending upon the availability of space in the raft system andupon the degree to which space in the flume is taken up by the growingpopulation. For example, under optimum temperature and nutrientconditions, the population of oysters doubles its space requirementsevery wwek, increasing in displacement volume by about 60 percent. Asthe seed grows from the sizes produced in the hatchery operation it isremoved from the trays and screened to size then kept separated whenreplaced into trays. Seed can be removed from the flume at A inch, inch,Azinch, diameter or larger sizes. The raft systems described can be usedto grow the seed to harvestable size, or to intermediate sizes fromwhich it can be transferred to other systems.

The embodiments of the invention in which a particular property orprivilege is claimed are defined as follows:

1. A floating raft utilizing the tide flow to furnish water containingnutrients to a dense population of free oyster or clam seed held in aplurality of trays within the raft comprising:

a frame structure adapted to be positioned transversely to the tide flowhaving an open rear end, a substantially closed front end, and bottomwall supports forming a plane sloping downwardly from the forward end ofthe raft towards the rear end thereof relative to the waterline,

flotation means secured to the frame structure for maintaining the upperportion of the raft at essentially water level,

retaining means for trays to be positioned in the raft,

a series of trays holding free oyster seed resting on the bottom wallsupports of the raft, each tray including a frame defining sidewalls anda foraminous bottom wall on the upper surface of which free oyster orclam seed rest,

baffles extending downwardly from the plane formed by the bottom wallsupports of the raft at spaced intervals and transverse to the tideflow, the depth of the baffles increasing from the forward end of theraft to the rear, for directing the tide flow containing nutrientsupwardly through the bottom walls of the trays, providing nutrients tothe seed and removing detrius therefrom; the water, after flowingthrough the seed, exiting through the open rear end of the raft.

2. The raft of claim 1 wherein the trays are stacked and nestedtogether.

3. The raft of claim 1 including water deflectors extending transverselyacross the front end and down the side walls of the raft preventingsubstantial water flow into the raft over the top of the trayspositioned therein.

4. The raft of claim 1 including a removable top cover for the raft.

5. The raft of claim 1 including vertical water deflectors extendingoutwardly from the sidewalls of the raft near the rear end thereof todeflect water flow along the sides of the raft outwardly and create apartial negative water pressure between the sidewalls at the rear end ofthe raft aiding water flow upwardly through the trays and out the rearend thereof, and aiding in positioning the raft in the tidal flow.

1. A floating raft utilizing the tide flow to furnish water containingnutrients to a dense population of free oyster or clam seed held in aplurality of trays within the raft comprising: a frame structure adaptedto be positioned transversely to the tide flow having an open rear end,a substantially closed front end, and bottom wall supports forming aplane sloping downwardly from the forward end of the raft towards therear end thereof relative to the water line, flotation means secured tothe frame structure for maintaining the upper portion of the raft atessentially water level, retaining means for trays to be positioned inthe raft, a series of trays holding free oyster seed resting on thebottom wall supports of the raft, each tray including a frame definingsidewalls and a foraminous bottom wall on the upper surface of whichfree oyster or clam seed rest, baffles extending downwardly from theplane formed by the bottom wall supports of the raft at spaced intervalsand transverse to the tide flow, the depth of the baffles increasingfrom the forward end of the raft to the rear, for directing the tideflow containing nutrients upwardly through the bottom walls of thetrays, providing nutrients to the seed and removing detrius therefrom;the water, after flowing through the seed, exiting through the open rearend of the raft.
 2. The raft of claim 1 wherein the trays are stackedand nested together.
 3. The raft of claim 1 including water deflectorsextending transversely across the front end and down the side walls ofthe raft preventing substantial water flow into the raft over the top ofthe trays positioned therein.
 4. The raft of claim 1 including aremovable top cover for the raft.
 5. The raft of claim 1 includingvertical water deflectors extending outwardly from the sidewalls of theraft near the rear end thereof to deflect water flow along the sides ofthe raft outwardly and create a partial negative water pressure betweenthe sidewalls at the rear end of the raft aiding water flow upwardlythrough the trays and out the rear end thereof, and aiding inpositioning the raft in the tidal flow.